Poor Knights marine reserve

the mystery of the social sting raysby Dr J Floor Anthoni (2007)
www.seafriends.org.nz/issues/res/pk/stingrays.htm

Stingrays have always fascinated people, not
just by their strange shapes and way of swimming, but mainly by their bad
reputation of stinging people. Indeed their sting can be quite painful,
and explorer Steve Irwin was killed by a sting piercing his heart. However,
my experience with stingrays has been quite the contrary: they are gentle
giants with enough intelligence to be playful. In New Zealand we have three
species, each of which has a unique character and lifestyle. My experience
has shown that you do not need to fear the stingrays of the Poor Knights.

Three species, three kindsIn New Zealand we have three species of stingray, the eagle ray, the
short-tailed stingray and the long-tailed stingray. It so happens that
all three can be encountered on the poor Knights, an unusual coincidence
because the eagle ray is mainly a coastal and estuarine stingray, and the
long-tailed stingray has reduced its range considerably in the past decade,
and can now mainly (only?) be found on the Poor Knights. It has disappeared
from coastal waters and is not found south of Auckland, although identification
guides still mention its southern range as Cook Strait (Wellington) and
its habitat as estuaries and muddy areas.

Sting rays belong to the 'primitive' cartilaginous fishes, as opposed
to the more 'modern' bony fishes, but in evolution they have in fact become
quite advanced. For instance they have internal fertilisation and bear
their young live. A female stingray has usually only two babies, which
after birth, have to fend for themselves. Contrary to the 'modern' fishes,
whose offspring float away on ocean currents, a stingray's babies are born
where the mother lives. This may explain why populations can maintain themselves
well in remote places like the Poor Knights Islands.
The difference between males and females can easily be seen as males
have two claspers trailing under their tail flap.

The eagle ray (Myliobatis
tenuicaudatus)The NZ eagle ray (Maori: Whai keo) can be distinguished quite easily
by its whip-like tail (tenuicaudatus=thin-tailed) looking like a
car antenna. At the base of this tail is of course found its sting, but
also a small back fin, which is absent in the two other species. The eagle
ray has a head and shoulders and pointed wings. It is usually grey to black
above with a white belly but can also be yellow-green to brown on top.

Eagle rays are found on both the North and South Island, mainly in coastal
areas and estuaries. It feeds mainly on molluscs, ranging from small cockles,
to scallops (coquilles St-Jacques) and on large snails like the Cooks turban
snail (Cookia sulcata). The eagle ray is generally shy and not playful.
It is entirely harmless and can be approached as far as it would let you.

On the Poor Knights, eagle rays are not very common. They must be feeding
from large snails like the Cooks turban snail, but I've never seen broken
fragments of such. The Poor Knights does not have cockles or scallops,
the preferred food of eagle rays.

f041228: on left a just-born baby eagle ray, about 40cm across.
It is dwarfed by the long-tailed stingray that startled it when passing
over. Baby eagle rays are very shy, but so cute with their blue spots.

f021002: the eagle ray (Myliobatis tenuicaudatus)
has a pronounced head. It also takes good care in burrowing itself well,
to remain invisible to predators like orca.

f034909: typical elegant flight of an eagle ray. This one
is yellowish rather than grey to black. It could well be albino.

f034912: The Poor Knights are inhabited also by a tribe of
yellow eagle rays like this female.

The short-tailed
stingray (Dasyatis brevicaudata)The short-tailed stingray could well be the most common one on the
Poor Knights and outer island of the east coast of the North Island, but
it is not common on the South Island. In places it grows as large as a
man, standing with outstretched arms, as can easily be measured from the
large imprints found in the sand. Bigger ones still have been seen (and
caught) with a wing span of up to 3.5m!

The short-tailed stingray is easily attracted to bait, and often appears
when fishermen gut their catch. Surprisingly, it can be hand-fed, as it
does not home in on its quarry by eyesight but by smell. It is intelligent
and learns quickly. Divers usually see the short-tailed stingray swimming
gently over the kelp as in the first photo, but it can move very fast.
It can speed in the opposite direction with a loud bang, caused by water
cavitating on its wing. In order to achieve this feat, it must be enormously
strong.

As scavenger, the short-tailed stingray must be able to find food easily
from occasional deaths in schooling fish.

f034915: this short-tailed stingray (Dasyatis brevicaudata)
is
well aware of the photographer who quietly let it pass by. Most would have
veered away by now.

f038733: a male short-tailed stingray shows its belly with
nostrils, mouth and gill slits. Trailing under its tail flap one can see
two claspers by which males are identified. Notice that short-tailed stingrays
have a grey margin underneath.

f022505: short-tailed stingrays are often encountered while
cruising in the warm layer just under the surface. That is where they can
be wounded by propellers, as happened to this poor stingray. Fortunately
they are able to survive large wounds.

f020509: several albino short-tailed stingrays can be encountered
at the Poor Knights Islands, like this female.

f029223: a medium-sized short-tailed stingray on the shallow
sand in Nursery Cove. Notice its squat shape and short tail with one or
two barbs.

The long-tailed
stingray (Dasyatis thetidis)The long-tailed stingray is dark olive to black on top and entirely
white underneath without a grey margin. It is immediately identified by
its very long tail, twice the length of its body. This stingray stays much
smaller than the short-tailed stingray, reaching a wing span of about 1m.
It can be approached easily as it is not aggressive. At the Poor Knights,
these stingrays can be found resting by day in the shallow sand of Nursery
Cove and the Labrid Channel.

f026017: a male long-tailed stingray (Dasyatis thetidis)
in flight.

f041227: a large female long-tailed stingray turns away from
the photographer, carefully avoiding her tail to make contact.

f012726: a highly pregnant female long-tailed stingray, one
baby on each side.

f012729: close-up of pregnant stingray shows that the pregnancy
bulge is quite large.

f029212: a snorkeldiver is allowed to touch a female long-tailed
stingray, but her tail is raised already for gently turning away.

f041511: two long-tailed stingrays on shallow sand and a
snorkeldiver passing cautiously over.

Socialising
in the archwaysThe Poor Knights have become famous for their socialising stingrays,
particularly those seen in Northern Arch. At one time I counted 53, and
on one of the photos below one can count as many as 26! But what are they
doing there?

There have been wild speculations about what brings these stingrays to
Northern Arch. It may have something to do with mating, as one finds most
in the mating months from September to November. But one does not find
them in other arches, except for Tie-dye Arch in The Squires, a considerable
distance away. Some think that they migrate from far away on the mainland,
to return later after mating. But for this, their numbers are not large
enough.

In recent years, scientists have made exaggerated claims about sharks'
and rays' ability of sensing electrical currents, to the extent that these
animals here in New Zealand could sense a car battery being dumped in the
sea at the other end of the ocean (10,000km away). This ability, it is
reasoned, enables them to read an internal compass to navigate from the
mainland to the Poor Knights and back.

f011933: five stingrays in Northern Arch on a day with poor
visibility. The one in centre is an albino.

f020507: looking up to the entrance, one can count 9 silhouettes.

f020528: this photo, taken with a 50mm lens, shows 26 stingrays
in Northern Arch.

The real reason for this behaviour is quite simple although also quite
unbelievable. Stingrays do not form pair bonds, and must therefore pair
up for mating, at the beginning of every year. Here in NZ, it happens in
spring, in the months September to November (not entirely sure of this).
Having dived on the Poor Knights since 1978, I have witnessed how it happened.
In the beginning, there were no stingrays in Northern Arch, but then one
day it began with only a couple. I observed that they were teaching themselves
how to hang-glide in the rising current. Stingrays have no swim bladders,
so they sink as soon as they stop swimming. But here they discovered that
they could stay suspended, without swimming.

The next year there were a few more, and the year thereafter a few more,
until one day I counted 53, half of whom were not quite capable of hang-gliding
yet, as they tried to figure out what the others were doing. The diagram
below shows the situation at Northern Arch, where currents rise over the
sil at the bottom, causing uplift. Along the sides, the currents speed
up, which can in theory also support hang-gliding, but this is very difficult
indeed. The best positions are somewhere towards the lower middle, and
there is some competition for these spots.

When the current stops, the fun is temporarily over, and one can see
them all just flapping around. No sooner has the current returned, and
the adept ones, take up their positions again. In Tie-dye Arch, which is
fully submerged and has a n extensive flat bottom, the currents distort
mainly at the top, where they exit. So one finds the stingrays hovering
here.

Diagram showing the uplifting current in Northern Arch, which
allows stingrays to hang-glide in place. In Northern Arch there is more
opportunity for hang-gliding than in Tie-dye Arch.

In Tie-dye arch, the water velocity distorts most near the
top, as the archway is fully submerged. So one finds stingrays hovering
near the top where the currents provide uplift.

f012701: the promontory of Northern Arch runs across the
current, which increases the current through the archway.

f218819: Tie-dye Arch is located under a gannet colony, with
its northern entrance on right. The archway is fully submerged.

Hovering in the current, or hang-gliding is not unique among stingrays,
although their aerodynamic shape is just so perfect for this, with large
horizontal planes. Many other fish species practice it, such as butterfly
perch, blue maomao, pink maomao, snapper, tarakihi, giant boarfish and
undoubtedly many more. For the photographer it offers a unique opportunity
to obtain a stationary shot of otherwise ever moving fish.

The photo below shows four young giant boarfish hang-gliding behind
a rocky wall at 20m depth. The biggest one just detached itself from the
strict formation that lined up their eye patches, as it comes for a closer
inspection. Notice their long backfin rays that shrink as they grow. Notice
also their large breast and hip fins, acting as ailerons (wing flaps).
There is also this poor tarakihi who by his lonesome sought company with
the boarfish on account of their superficial resemblance by a dark patch.
The tarakihi is closely related to the porae, both having long breast fins
that could act as ailerons.

f006124: four young giant boarfish (Paristiopterus labiosus)
and one tarakihi (Nemadactylus macropterus) hovering in the current
deflected by the rocky wall on right. Note that young boarfish have long
fins that shrink as they grow older!

Other encountersAs an underwater photographer, I am privileged to be able to document
many experiences. As every photographer knows, what makes it to film is
only a small part of the total experience, and there remains much just
recorded by the grey matter in one's mind. Yet these experiences need to
be told, so that a more complete picture emerges of diving in New Zealand
and the Poor Knights.

The smart kingfish and the decoy rayIn Nursery Cove I was watching a young kingfish, no larger than 50cm,
hunt a school of young koheru. In this he was spectacularly unsuccessful,
as these fish dodged him and even out-swam him at every lunge he made for
them. This in itself is astounding, because the laws of physics insist
that small fish cannot outswim larger ones. Yet they did, and with a wide
margin.

When koheru are catching morsels of food, they are in a loose schooling
formation, but as soon as panic arises, they group into a tight oval ball
which acts like a much larger fish, propelled by a mysterious jet motor.
The principle of a jet motor is that its thrust equals the amount of water
jetted out, multiplied by speed. Apparently the little fish, by moving
their tails and bodies in unison, are capable of pumping a strong thrust
that moves them forward with least friction, while also satisfying the
laws of physics for bigger fish. They outswim the larger kingfish as it
is not jet-propelled.

This shows clearly why it is necessary for kingfish to hunt in packs,
for this causes confusion amongst its prey, and like wolves, the kingfish
can surround the school of little fishes.

Now, this little Kingfish became visibly tired and disappeared, only
to reappear hiding underneath a long-tailed stingray (see photo). His plan
would have worked had the stingray not been annoyed with this object underneath,
that prevented it from landing on the sand. So it began to shear tightly
over the stalked kelp, trying to rub the little blighter off. All this
foiled the little kingfish' plan, although he was nearly successful.

f023206: a young kingfish uses a long-tailed stingray as
trojan horse to attack a school of koheru, shown as light patches in the
distance.

How can little fishes outswim much larger predators? Could
it be that by swimming in close quarters, they produce a jet motor, as
yet unknown to Man?

The giant short-tailed stingrayDuring a lonely dive at the Mokohinau Islands, at the northernmost
tip of Burgess, where an exposed canyon loops around a large rock, it was
rather dark due to all the foam on top. And as I swam over the egg-sized
loose pebbles, the bottom changed into smooth rock, and then pebbles again.
It took me quite a while to realise that this smooth rock was rather unusual.
As I turned around, I saw that I had been swimming right over the back
of a gigantic stingray, so big that I could not believe (comprehend, really)
what I saw.

It was a large female short-tailed stingray with a wing span of at least
3.5m! She was not concerned with my presence at all, as I approached cautiously
from behind, where I could film only part of her due to all the suspended
bubbles and consequent darkness. The base of her tail was thicker than
a dive tank. Her barb was 60cm (2ft) long, and at the base of this spine
I could not get my index and thumb to meet. Such a giant is perhaps over
100 years old, and one would hope she would survive another century. Imagine
such a friendly giant living at the Poor Knights, always sleeping in her
preferred den, and often visited by divers?

I'd like to share with you the internal turmoil
inside me when I finally realised what I was looking at. First I swam squarely
over the back of this stingray, thinking it was a rock. Then 4 metres further,
it dawned upon me that the smooth rock I saw, was strange. I stopped and
looked back and I didn't see the stingray. I backtracked to touching distance
and still didn't see it. My mind could not see it because it didn't match
any of the previous images of stingrays in my mind. I couldn't see it because
it was so big. Yet, the tail was there, like one that stingrays have. Then
finally my brain began to accept a new dimension and slowly I could see
the rock for a sting ray. And guess what? A wave of emotion overcame me
- not fear at all - but a kind of emotional discharge like when firmly
held belief is proved wrong, and finally accepting the truth. I began to
snotter for no apparent reason.Apparently our brains are resisting anything that overturns
previous experiences. Apparently our eyes can see only what we expect to
see, and as soon as it differs by a whole dimension, we can not see it.
And when we finally come to grips with it, it goes with strong emotions.
Think about this when going into a new environment, like diving.

The stingray
who fell in love with a diverMy buddy and I were diving on the sand on the southern end of The Labyrinth
when we noticed three young female long-tailed stingrays on the sand. Nothing
special, except that these pointed their stiff tails right up, instead
of holding them down over the sand. Ignoring them, we busied ourselves
filming a sharp-nosed pufferfish, when one of the rays came really close.

She snuggled up to Bruce, touching and caressing him, and we both returned
the favour. The other two stingrays also came closer for a cuddle. What
did we deserve for such affection? These female stingrays still pointed
their tails stiff up, and snuggled up against us, not planning any time
soon to leave. What was going on?

Back on the boat we couldn't get over our surprise and excitement, trying
to explain what we had experienced. The closest explanation is that these
young female stingrays were somehow on heat and mistook us for mating partners.
Hunters have often reported that young does (female deer) in their first
season on heat, come snuggling up to them, quite overwhelmed by feelings
inside, yet not knowing what to do. Perhaps this was also the case with
our stingray girls?

Riding a stingrayOn the sandy patch between Ngaio Rock and the Natural Bridge, longtailed
stingrays sleep after a night's loveplay. We have always wondered whether
one could play with these animals, like holding one by its tail and 'riding
its tail' by steering it. The crucial bit comes in two steps: first you
must approach without the stingray scurrying away. Instilling trust is
a slow process that can easily go too fast, resulting in flight. We had
seven stingrays here, so perhaps one would be brave and willing.

The second step is that you must somehow convey a sense of playfulness,
touching without meaning harm. To do this, you must not be overbearing,
but touch a little bit, then retreat, come back and do it again, much the
way a cat would do to another cat - teasing. After five failures, the third
ray made a bold move and returned after his flight. A little male, he placed
himself right between us, me with the camera and Bruce as actor. Bruce
touched it here and there, and lo - the ray touched back. Bruce could slide
his hand and arm underneath and lift the ray up. From here it was so easy.
He loosely held the ray by its tail, and both swam through the Labrid Channel,
while the cameraman could hardly keep up with them. Then I tapped Bruce
on the shoulder to let go. He thought I was a spoilsport at the time. But
the ray turned back and came for more. It then gradually led us the other
way to beyond diving depth and we had to let it go for an unplanned hasty
ascent.

I have done this once more since, on a lonely dive without bystanders
and cameras. What an experience. To imagine a totally wild animal, very
much smaller than me, having enough sense to understand what play is, and
then enough courage to give it a go!

Feeding the stingrays in the Garden
of Eden, MokohinauA German visitor once wanted to swim with dolphins - no problem. On
average, one encounters a pod once every 15-20 nautical miles, so we set
out on a tour from Leigh via Kawau, past Little Barrier, skirting Great
Barrier and ending up at the Mokohinaus. No dolphins in a hundred nautical
miles!

We ended up diving and decompressing in the Garden of Eden, a sheltered
cove at the Mokohinau Islands, Burgess Island. It is a wonderful place
that gave me many memorable encounters. While snorkelling, I discovered
two big short-tailed stingrays, which was not anything spectacular. But
back in the boat, my visitor asked whether I had seen anything special.
"No, just two stingrays". He almost exploded: "Wass, zwei Roggen?". Apparently
these animals have elsewhere quite some reputation. Suddenly his lack of
enthusiasm turned into a stampede to get back in the water.

And yes, the Roggen were still there. I noticed that they were looking
for something, and then that a yacht was filleting its snapper catch above,
the carcass frames raining down. But the rays were seeking by smell rather
than by sight. So I took a couple of carcasses and held one up. After three
overflights, one ray got the message and took the frame from my hand, ever
so gently. Rather than swallowing it as other fish would, its jaws crunched
the skeleton like a mulcher would. All the while the ray fluttered around.
Once it had completely crunched the meal, it came back for more. In the
meantime, the second ray had learnt the routine. My German friend was over
the moon, and as he had a video camera, returned home very satisfied. Sorry
for the lack of dolphins.

For myself, it was a lesson in how quick completely wild animals can
overcome their fears, and then learn something they have never done before
in their lives. It taught me never to underestimate stingrays. It was also
the beginning of my suspicion that there is something entirely wrong with
the sea. For where have all those dolphins gone?

The spearo attackAfter the Goat Island marine reserve was opened, researchers often
took their raw material from the reserve, and if this was fish, it needed
to be speared selectively (The Department of Conservation did not exist
back then). One young scientist was particularly good at that, and often
did the work for others.

Now you must remember that the act of spearfishing is quite demanding,
and that it is quite an honour to be good at it. In those days, things
were done rather pioneeringly, and the spearfisher (spearo) stored the
speared fish on a ring attached to his weight belt. We know that this is
not a good idea, because the bleeding fish can attract larger fish, like
sharks. So a freediving spearo attaches the ring to a float, trailing it
some 40 metres behind (this is the depth he can go to). But what do you
do when you are spearing for science on a SCUBA lung? You hang the fish
off your belt, of course!

So this scienctific-spearo had been sniffed by a large stingray, and
as he was surfacing, suddenly the whole world went dark as this stingray
wrapped himself around the diver with its large wings, and would not let
go. The story is that the spearo peed in his pants, because he was unable
to move his hands and could not reach for his knife. Several frightening
minutes passed until finally the ray let go. Fortunately this spearo was
very experienced and did not panic. And the fish? The ray took the lot!

The Cayman Island stingrays,
the experience of George Wauchope

Most people hold the misinformed view that stingrays are dangerous creatures
that must be avoided at all costs. This is simply not accurate. This irrational
fear mainly stems from the infamous death of Steve Irwin (the “Crocodile
Hunter”) on the 4th September 2006. Many people believe that since Irwin
was killed by a stingray, that all stingrays are dangerous, but this could
not be further from the truth.
There are over 200 species of stingrays in the world, and the vast
majority pose no threat to humans. Steve Irwin was killed in a freak accident
where the ray felt cornered and responded with force.

The Cayman Islands are a group of three small islands in the Caribbean.
Here are many species of Stingrays, all of which are completely safe. The
“Southern Stingray” is found throughout the Caribbean and lives a peaceful
and docile life. Grand Cayman is home to “Stingray City”, which is the
pinnacle of human-stingray interaction. This is a shallow sandbar (2-3
feet deep) where you can hand-feed the Southern Rays. Thousands of tourists
flock here every year, and virtually no one has issues. There are extremely
rare occurrences where a stingray’s barb cuts someone, inducing short term,
non-life threatening damage; however, these situations are always caused
by people stepping on the rays through careless behavior.

Most people who visit “Stingray City” are scared at first, because Steve
Irwin’s experience lurks in the back of their minds; however, as soon as
they enter the warm shallow water, they realize there is no threat posed
by the rays.
These Southern Stingrays can grow up to 5 feet in diameter, and spend
most of their time feeding on the sea-floor, sifting through sand to find
small crustaceans. These stingrays provide massive economic benefits to
the Cayman Islands through the tourism it attracts; estimates show that
Stingray City brings over $30 million USD per year to the Cayman economy.
The reputation stingrays have earned over the last decade, mainly due to
Irwin’s death, is not justified, and it’s time that people realized this.